A 35 year old lady presents following an episode of rapid, regular palpitations felt as a "rapid pounding sensation in her neck", which was abrupt in onset, lasted for around 20 minutes and terminated suddenly, without treatment. She is also polyuric. The paramedics obtained an ECG during the episode.
She has experienced a few shorter but similar episodes during the last 2 to 3 months. She is otherwise healthy and is not on any drugs.